Optical navigation sensors are conventionally used for surface navigation in an input device such as an optical mouse. A conventional input device tracks the relative movement between a navigation surface and an image sensor within the input device. Light is illuminated towards the navigation surface or a target object by a light source. In general, images of the illuminated navigation surface or multiple frames of digital image data of the illuminated target object are captured by the sensor and subsequently processed and further translated as a cursor movement on the input device.
More recently, optical finger navigation devices have been widely used in many portable handheld devices, such as a mobile handset. An optical finger navigation device permits the user to manipulate the navigation function by simply moving a finger on a finger interface surface of such a portable device. In contrast to a conventional optical mouse system, an optical finger navigation device uses a light source to illuminate the user's finger. The general operational concept of an optical finger navigation device is similar to a conventional optical mouse, except that the sensor incorporated in for finger navigation is generally positioned facing upward from the device, rather than downward. In addition, the tracking surface for the optical finger navigation system is a user's finger, instead of a desktop work surface.
With an optical finger navigation device that is manually manipulated, there is a need to recognize when the finger has been lifted off the navigation surface. For the purpose of power saving, as well as preventing cursor skating, it is important to have the navigation operation be temporarily suspended when the finger has been lifted off the navigation surface. There are conventional lift detection systems or object detection systems that can be implemented in order to prevent the input device from tracking that may be based on image defocus or image surface quality value. However, these systems typically involve complex design and are usually integrated as part of the navigation system during the chip design. Furthermore, some object detection systems may require the sensor to capture multiple images for comparison; which would require the LED to be turned on at all times.
Another known limitation of many finger navigation devices is the unintended cursor movement when a finger is initially placed on the navigation surface, or as it is being lifted off the navigation surface. Such placing and lifting of a finger can cause unintended cursor jittering, unintended cursor movement, or sudden jump of the cursor.